Methods for producing an etch resist pattern on a metallic surface

ABSTRACT

A method of forming a metallic pattern on a substrate is provided. The method includes applying onto a metallic surface, a chemically surface- activating solution having an activating agent that chemically activates the metallic surface; non-impact printing an etch-resist ink on the activated surface to produce an etch resist mask according to a predetermined pattern, wherein at least one ink component within the etch-resist ink undergoes a chemical reaction with the activated metallic surface to immobilize droplets of the etch-resist ink when hitting the activated surface; performing an etching process to remove unmasked metallic portions that are not covered with the etch resist mask; and removing the etch resist mask.

FIELD OF THE INVENTION

Embodiments of the invention relates to manufacturing of printed circuitboards by applying the etch-resist mask using nonimpact orienting, suchas, inkjet printing.

BACKGROUND

Printed circuit boards (PCBs) are widely used in most electronicproducts. The manufacturing of PCBs is considered cheaper, faster andmore accurate than using other wiring methods such as point-to-pointconstruction. Still, there is an ongoing search for simpler and morecost-effective manufacturing processes that would maintain high qualityand would enable to produce PCBs according to specific requirementsincluding the manufacturing of cost-effective smaller batches, largerbatches with high throughput, on-demand boards, boards with densercircuits, boards with thinner lines and others.

The patterning of copper lines in the manufacturing process of a PCB isusually done by applying an etch-resist photo-mask on a copper layerlaminated to an insulating material board and removing exposed copperportions by an etching process, leaving only the desired copper lines(also refer to as image patterning) as the electrically conductingpaths. The etch-resist pattern can be applied on top of the copper layerby additive methods, for example by non-impact printing (e.g. inkjetprinting) on top of the copper layer. Conventional inkjet materials haverelatively low viscosity and accordingly when ink drops would hit anon-absorbing surface, such as a copper surface, uncontrolled spreadingof the drops and other phenomena such as clustering, coalescence andextensive dot gain usually occur. Accordingly, the printed pattern,which is formed by inkjet printing technology, may exhibit poor qualityor the copper lines including, for example, lack of details,inconsistent line width, poor line edge smoothness, shorts betweenadjacent lines and disconnection of pattern lines.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 is flowchart of a method for producing an etch-resist maskaccording to some embodiments of the invention; and

FIG. 2A shows a photograph of an exemplary etch resist mask printed on anon-activated copper; and

FIG. 2B shows photographs of an exemplary etch resist mask printed on anactivated copper surface according to embodiments of the invention.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate corresponding or analogous elements.

SUMMERY

Embodiments of the invention include methods of forming a metallicpattern on a substrate. The method may include applying onto a metallicsurface coupled to the substrate, a chemically surface-activatingsolution having an activating agent that chemically activates themetallic surface; non-impact printing an etch-resist ink on theactivated surface to produce an etch resist mask according to apredetermined pattern, wherein at least one ink component within theetch-resist ink undergoes a chemical reaction with the activatedmetallic surface to immobilize droplets of the etch-resist ink whenhitting the activated surface; performing an etching process to removeunmasked metallic portions that are not covered with the etch resistmask; and removing the etch resist mask.

In some embodiments, the metallic pattern formed according toembodiments of the inventions includes pattern lines having a width ofless than 50 microns. In some embodiments, the etch resist maskedproduced according to embodiments of the invention includes lines havinga width of less than 50 microns. In some embodiments, the metallicpattern formed according to embodiments of the inventions includespattern lines having a width of less than 30 microns. In someembodiments, the etch resist masked produced according to embodiments ofthe invention includes lines having a width of less than 30 microns.

In some embodiment, the method may include, prior to printing, removingthe chemically surface-activating solution from the surface using asolvent. In some embodiments, the ink component that undergoes thechemical reaction is an anionic component. In some embodiments, the inkcomponent that undergoes the chemical reaction with the activatedsurface is a polymeric component selected from an acrylate, a phosphate,a sulfonate or a mixture thereof. In some embodiments, the activatingagent may comprise at least one of copper salts, ferric salts,chromic-sulfuric acids, persulfate salts, sodium chlorite and hydrogenperoxide or a mixture thereof.

In some embodiments, applying the chemically surface-activating solutioncomprises immersing the metallic surface into a bath containing thechemically surface-activating solution for about 10-60 seconds. In someembodiments, applying the chemically surface-activating solutioncomprises spraying the chemically surface-activating solution onto themetallic. In some embodiments, non-impact printing the etch-resist inkon the activated surface comprises ink-jet printing

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, and components have notbeen described in detail so as not to obscure the present invention.

Embodiments of the invention are related to methods of forming orapplying an etch-resist mask on a metallic layer by non-impact printing,for example, during the manufacturing of printed circuit boards (PCBs).A method of applying an etch-resist mask on a metallic surface accordingto embodiments of the invention may include applying a chemicallysurface-activating solution on top of a metallic surface to chemicallyactivate the metallic surface, followed by removing/washing thechemically activating solution from the surface and printing (e.g.inkjet printing) an etch resist ink on top of the activated surface.According to embodiments of the invention, a reactive component of theetch-resist ink undergoes a chemical reaction with the activated surfaceto immobilize droplets of the liquid composition when hitting thesurface. The chemical reaction may cause a significant increase in theink droplet viscosity (for example, by one or two orders of magnitudes)instantaneously upon hitting the activated surface.

In some embodiments, the reactive component in the etch-resist ink (inkcomponent) may be an etch resist component and in other embodiments thereactive component may be different from the etch-resist component.According to some embodiments, more than one reactive component of theetch resist-ink may undergo a chemical reaction with components on theactivated surface.

The metallic layer may be a copper layer laminated onto an insulatingnon-conductive substrate. For ease of explanation, the description belowrefers to a copper surface. It should be realized that other metallicsurfaces, such as, aluminum surfaces, stainless steel surfaces, goldsurfaces and others are likewise applicable to embodiments of theinvention.

Reference is made to FIG. 1, which is a flowchart of a method ofproducing an etch-resist mask according to some embodiments of theinvention. According to embodiments of the invention, as illustrated inbox 110, the method may include applying a chemically surface-activatingsolution onto a metallic surface, on which an etch-resist pattern is tobe printed. In some embodiments, the chemically surface-activatingsolution may be or may include any etching solution capable tochemically activate the surface. A chemically activated surface may bedefined as a surface which, prior to the surface activation, will notreact with the etch resist ink materials while it does react post thesurface activation to cause the immobilization of the etch resist inkdroplet. The surface-activating solution may include, for example,copper salts, ferric salts, chromic-sulfuric acids, persulfate salts,sodium chlorite and hydrogen peroxide. In some embodiments, applying achemically activating solution may include immersing the surface in abath containing the chemically surface-activating solution, spraying thechemically surface-activating solution over the surface and any othersuitable method. In some embodiments, the method may include subjectingthe metallic surface to the chemically activating solution (e.g., byimmersing, spraying or the like) for a predetermined amount of time, forexample, for 10 seconds, 20 seconds, 30 seconds, 60 seconds or more.

As illustrated in box 115, in some embodiments, the method may includeoptionally, removing the chemically surface-activating solution using,for example, an alcoholic solution. For example, the method may includeremoving residues of the chemically surface-activating solution from thesurface using ethanol. In some embodiments, removing the chemicallyactivating solution from the surface may be done using liquids otherthan alcoholic solutions, for example; propyl alcohol; iso-propylalcohol; acetone.

As illustrated in box 120, in some embodiments, the method may includenon-impact printing (e.g., by inkjet printing) an etch-resist ink ontothe activated surface to produce an etch resist mask according to apredetermined pattern. The etch resist ink may comprise an etch-resistpolymeric component that undergoes a chemical reaction with theactivated surface to immobilize droplets of the etch-resist ink whenhitting the activated surface. In some embodiments, another inkcomponent, different from the etch-resist component, undergoes achemical reaction with the activated surface to immobilize droplets ofthe etch-resist ink when hitting the activated surface.

Non-limiting examples of etch resist polymeric reactive components maybe acrylates, styrene acrylates, phosphates and sulfonates polymers,obtaining molecular weight (Mw) form 1000-17,000.

In some embodiments, the etch resist reactive polymeric component may bewater-soluble and may include reactive anionic components. Non-limitingexamples of anionic etch-resist reactive component may include at leastone anionic polymer (in a base form) at pH higher than 7.0. The anionicpolymer may be selected from acrylic resins and styrene-acrylic resinsin their dissolved salt forms, sulphonic resins in their dissolved saltform, such as sodium, ammonium or amine neutralized form or the like.Without wishing to be bound by any specific theoretical mechanism, theaforementioned resins may undergo a reaction with the reactive(activated) surface. For example, the copper metal surface is activatedto form copper cations on top of the copper and when an acrylic polymer(being in the etch-resist ink) would hit the surface, the anionicacrylate may react with the copper ions to form a polymeric matrix inthe droplet, which would dramatically increase the droplet viscosity.

In some embodiments, the ink component that undergoes the chemicalreaction with a surface-activated component to immobilize droplets ofthe etch-resist ink when hitting the activated surface may be differentfrom the etch-resist component.

As illustrated in box 130, the masked copper board may further be etchedby a metal etching (e.g., acidic copper etching) solution to removeexposed, unmasked portions of the metallic layer. As illustrated in box140, the etch resist mask may then be removed to expose a line patternon the substrate, i.e., an insulating board.

EXAMPLES

Using an Epson stylus 4900 inkjet printer, exemplary liquid compositions(etch-resist ink compositions as described herein) were printed on anFR4 copper clad board having a copper thickness of 18 micron. In sometests, the copper was first chemically activated by applying achemically surface-activating solution to activate the copper surface. Aliquid composition of an etch resist ink was selectively printedaccording to a predetermined pattern on top of either the activated orinactivated copper surface, using ink-jet printing technology. In thedescription below, % (w/w) is a measure of the concentration of asubstance in terms of the percentage by weight relative to the weight ofthe composition. Copper from the unmasked exposed zones was etched awayusing an etchant bath containing a ferric chloride etchant solution ofstrength 42° Baume supplied by Amza (PERMIX 166). The etching wasperformed in a Spray Developer S31, supplied by Walter Lemmen GMBH, at atemperature of 35° C. for 3 minutes. The etch resist mask was strippedoff by immersing the etched board in a 1% (w/w) aqueous solution of NaOHat a temperature of 25° C. followed by washing the FR4 copper board withwater and drying by air at 25° C.

Example 1

An etch resist ink, which is in a form of a liquid composition at roomtemperature, was printed on top of an untreated (inactivated) copper FR4board. The liquid composition was prepared with 10% propylene glycol (asa humectant) and 1% (w/w) 2-Amino-2-methyl propanol, 0.3% (w/w) of BYK348 supplied by BYK and 2% (w/w) of Bayscript BA Cyan. These materialswere dissolved in water containing 24% Joncryl 8085 styrene acrylicresin solution. Using an Epson stylus 4900 inkjet printer the etchresist composition was printed on top of an FR4 copper clad board havinga copper thickness of 18 micron, to produce the etch resist mask.

The etch-resist mask was visually inspected. As can be shown in FIG. 2A,the printed pattern demonstrated very poor print quality with extremelypoor edge definitions and severe shorts between the lines.

Example 2

The liquid composition was prepared as detailed in Example 1. FR4 copperclad board surface was activated by dipping (e.g., immersing) the copperclad into an aqueous solution of CuCl₂ 0.5% (w/w) for 30 secondsfollowed by washing the copper board with technical ethanol.

Using an Epson stylus 4900 inkjet printer, the liquid composition wasprinted on top of the treated copper board and dried at 80° C. toproduce an insoluble etch resist mask. The etch resist patterndemonstrated a high print quality well-defined and thin lines width downto 50 micrometers contained sharp edges and no line breaks as can beshown in FIG. 2B. Etching of the exposed copper and removal of the etchresist mask were conducted as detailed in Example 1. The wiring patternon the board demonstrated well-defined thin lines with a width down to50 microns containing sharp edges and no line breaks.

Example 3

The liquid composition was prepared as detailed in Example 1. The coppersurface was activated by dipping the FR4 copper clad board into a bathcontaining 20% aqueous solution of FeCl₃ (w/w) for 10 sec following bywashing the copper board with technical ethanol.

Similarly to Example 2, the liquid composition was inkjet-printed on thecoated copper board and dried at 80° C. to produce an insoluble etchresist mask. The etch resist pattern demonstrated a high print qualitywell-defined and thin lines down to 50 micron contained sharp edges andno line breaks. Etching of the exposed copper and removal of the etchresist mask were conducted as detailed in Example 1. The wiring patternon the board demonstrated well-defined pattern with thin lines having awidth of down to 30 micron sharp edges and no line breaks.

Example 4

The liquid composition was prepared as detailed in Example 1. The coppersurface was activated by dipping the FR4 copper clad board into anaqueous solution of Na₂S₂O₈ 1% (w/w) for 30 sec following by washing thecopper board with technical ethanol.

Using an Epson stylus 4900 inkjet printer, the etch resist liquidcomposition was printed on the treated copper board and dried at 80° C.to produce an insoluble etch resist mask. The etch resist patterndemonstrated a high print quality well-defined and thin lines down to 50micrometers, contained sharp edges and no line breaks. The etching ofthe unmasked copper and removal of the etch resist mask were conductedas detailed in example 1. The wiring pattern produced by the etching andstripping processes demonstrated a well-defined pattern with thin lineshaving a width of down to 30 micron sharp edges and no line breaks.

Table 1 below lists some non-limiting examples of chemicallysurface-activating components used in embodiments of the invention,their relative weigh concentrations in the surface-activating solutionand suggested immersing time according to some embodiments of theinvention.

TABLE 1 Activating Concentration immersing time agent (w/w %) (Seconds)CuCl₂ (or any 0.5-1 30 divalent copper salts) Na₂S₂O₈ (or any 0.5-1 30per-sulfate salt) H₂O₂ 10 30 FeCl₃ 20 10 HCrO₄/H₂SO₄ 5 30 NaClO₂ 5 60

Table 2 below lists some non-limiting examples of etch-resist inks.

TABLE 2 Etch-resist Etch-resist ink component 1 2% (w/w) of Cyan dye,10% acrylates propylene glycol, 1% (w/w) 2-Amino- polymers; 2-methylpropanol and 0.3% (w/w) of Mw: 1000- surfactant were dissolved in water17,000 containing 24% styrene acrylic resin solution. 2 2% (w/w) of Cyandye, 10% Phosphates propylene glycol, 1% (w/w) 2-Amino- polymers2-methyl propanol and 0.3% (w/w) of Mw: 500- surfactant were dissolvedin water 17,000 containing 24% phosphates resin solution. 3 2% (w/w) ofCyan dye, 10% Sulfonates propylene glycol, 1% (w/w) 2-Amino- polymers2-methyl propanol and 0.3% (w/w) of Mw: 500- surfactant were dissolvedin water 17,000 containing 24% sulfonates resin solution.

While certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes, andequivalents will now occur to those of ordinary skill in the art. It is,therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the invention.

1. A method of forming a metallic pattern on a substrate, the methodcomprising: applying onto a metallic surface coupled to the substrate, achemically surface-activating solution having an activating agent thatchemically activates the metallic surface; non-impact printing anetch-resist ink on the activated surface to produce an etch resist maskaccording to a predetermined pattern, wherein at least one ink componentwithin the etch-resist ink undergoes a chemical reaction with theactivated metallic surface to immobilize droplets of the etch-resist inkwhen hitting the activated surface; performing an etching process toremove unmasked metallic portions that are not covered with the etchresist mask; and removing the etch resist mask.
 2. The method of claim1, wherein the metallic pattern includes metallic lines having a widthof less than 50 microns.
 3. The method of claim 1, wherein the etchresist mask includes lines having a width of less than 50 microns. 4.The method of claim 1, wherein the metallic pattern includes metalliclines having a width of less than 30 microns.
 5. The method of claim 1,wherein the etch resist mask includes lines having a width of less than30 microns.
 6. The method of claim 1, wherein prior to printing,removing the chemically surface-activating solution from the surfaceusing a solvent.
 7. The method of claim 1, wherein the ink componentthat undergoes the chemical reaction is an anionic component.
 8. Themethod of claim 1, wherein the ink component that undergoes the chemicalreaction with the activated surface is a polymeric component selectedfrom an acrylate, a phosphate, a sulfonate or a mixture thereof.
 9. Themethod of claim 1, wherein the activating agent comprises at least oneof copper salts, ferric salts, chromic-sulfuric acids, persulfate salts,sodium chlorite and hydrogen peroxide or a mixture thereof.
 10. Themethod of claim 1, wherein applying the chemically surface-activatingsolution comprises immersing the metallic surface into a bath containingthe chemically surface-activating solution for about 10-60 seconds. 11.The method of claim 1, wherein applying the chemicallysurface-activating solution comprises spraying the chemicallysurface-activating solution onto the metallic.
 12. The method of claim1, wherein non-impact printing the etch-resist ink on the activatedsurface comprises ink-jet printing.